The present invention relates to the production of hydrogen by steam reforming, and provides a compact heat exchanger capable of supporting all of the functions required in a catalytic steam reforming process.
The hydrogen produced by the present invention is intended to be used to operate a fuel cell. A fuel cell consumes hydrogen while producing electric power.
Steam reforming refers to the endothermic reaction whereby hydrogen is produced from methane, or from some other hydrocarbon. The steam reforming reaction, when the fuel is methane, is as follows:CH4+H2O→CO+3H2
For reforming a C8 hydrocarbon, the reaction is:C8H18+8H2O→8CO+17H2
If the fuel cell is to be used to power a vehicle, the fuel cell, and the steam reformer used to supply hydrogen to the fuel cell, must be compact. Also, steps must be taken to reduce or eliminate the carbon monoxide products, which will quickly poison the membrane in the fuel cell.
Because the steam reforming reaction is endothermic, the steam reforming reaction must have a source of heat. Therefore, building a steam reformer involves construction of a heat exchanger suitable for supplying heat for the reaction.
It has been proposed to provide a heat exchanger formed of a strip of metal that has been folded back and forth upon itself. Examples of such heat exchangers are provided in copending patent application Ser. No. 10/417,410 and copending patent application Ser. No. 10/812,506, the disclosures of which are hereby incorporated by reference.
In the above-cited applications, the heat exchanger is configured such that heat can be exchanged between only two fluid streams. The present invention has, as its major component, a heat exchanger, also formed of a folded strip, but this heat exchanger enables heat transfer among three or more fluid streams. By combining various heat exchange operations in a single heat exchanger, the hydrogen generator of the present invention achieves the objective of producing hydrogen within a relatively compact space.